1. Field of the Invention
The present invention relates to a power system for a vehicle comprising a swash plate type oil hydrostatic non-stage transmission, and particularly to an advantageous layout of a ratio change mechanism in the swash plate type oil hydrostatic non-stage transmission.
2. Description of Background Art
A swash plate type oil hydrostatic non-stage transmission in which an oil hydraulic pump on the input side and an oil hydraulic motor on the output side are disposed coaxially and connected to each other by an oil hydraulic circuit wherein the volume ratio of the oil hydraulic pump and the oil hydraulic motor is varied to enable non-stage speed change. The inclination angle of a speed change swash plate is provided coaxially with the oil hydraulic pump and the oil hydraulic motor and is varied by a ratio change mechanism to thereby vary the change gear ratio. (See, for example, Japanese Patent Publications No. Hei 7-23746 and No. Hei 8-26930).
FIG. 7 is a general view showing a swash plate type oil hydrostatic non-stage transmission according to the prior art, as viewed from the speed change shaft direction. In FIG. 7, a lower end portion of a cylinder 202 is fitted to an upper end portion of a crank chamber wall 201 formed in a crank case 200 to form a mating plane P1, and the cylinder axis C10 is orthogonal to the mating plane P. The cylinder axis C10 is the center line of the cylinder bore.
A transmission fixing wall 203 is provided in the crank case 202 on the outside of the crank chamber, and a turning shaft 205 formed as a part of and integrally with a speed change swash plate 204 is turnably supported on the wall 203. One end of a main body portion 206 of the swash plate type oil hydrostatic non-stage transmission is in slidable contact with the speed change swash plate 204, and a changed speed is outputted from a speed change shaft 207.
A ratio change mechanism disposed on a lateral side of the main body portion 206 comprises the speed change swash plate 204, a slider 210 connected through a shaft 209 to a projected portion 208 formed on the speed change swash plate 204, and a ratio change driving shaft 211 supporting the slider 210. The ratio change driving shaft 211 is a ball screw disposed in parallel with the speed change shaft 207 and driven to rotate by a motor (not shown), and rotation of the ball screw causes the slider 210 to move in the axial direction, whereby the inclination angle of the speed change swash plate 204 is varied.
Further, in order to detect the turning angle of the speed change swash plate 204, a ratio detecting sensor 212 is fitted to the transmission fixing wall 203 on the lower side of the main body portion 206. The ratio detecting sensor 212 is a potentiometer, of which a detecting shaft 213 serving as a detecting portion projects to the upper side and is connected to the turning shaft 205 of the speed change swash plate 204, and is turned around the axis by the same turning angle as the speed change swash plate 204 to thereby detect the turning angle of the speed change swash plate 204.
For simplifying the structure of the ratio detecting sensor 212, it is necessary that the detecting shaft 213 can directly detect the turning of the speed change swash plate 204, and, therefore, the axis of the detecting shaft 213 is disposed coaxially with the axis C11 of the turning shaft 205. Further, the axes of the detecting shaft 213 and C11 are roughly orthogonal to a line segment L1 connected between the centers O11 and O12 of the speed change shaft 207 and the ratio change driving shaft 211, and are inclined relative to the cylinder axis C10. In addition, the line segment L1 also skewly intersects the cylinder axis C10, and is inclined relative to the mating plane P1.
Meanwhile, in the power transmission device constituted as above, the axis of the detecting shaft 213 serves also as a fitting axis of the ratio detecting sensor 212. In the prior art, there is no special consideration on the direction of the fitting axis of the detecting shaft 213, and the fitting axis of the detecting shaft 213 is inclined relative to the mating plane P1 of the crank case and the cylinder. Since the fitting axis of the detecting shaft 213 and the cylinder axis C10 are different in direction, mechanical working or machining after formation of the crank case 200 by the casting or the like is carried out as follows. First, the inside of the crank chamber is machined in parallel to the cylinder axis C10 from the side of the mating plane P1 of the crank case and the cylinder, and then a fitting portion for the ratio detecting sensor 212 is machined; in this case, the machining axes of the two machining operations differ from each other.
As a result, in actual machining, the crank case 200 is positioned on jigs so that the machining axis of a machining device (not shown) coincides with the cylinder axis C10, then machining of the crank chamber is carried out, thereafter the machining is stopped, and the crank case must be repositioned on jigs so that the machining axis (C12) for the fitting portion for the ratio detecting sensor 212 coincides with the machining axis of the machining device, before the fitting portion for the ratio detecting sensor is machined. Therefore, the machining process takes much time and labor, and enhancement of workability is requested. Accordingly, it is an object of the present invention to solve such problems.
In order to solve the above-mentioned problems, the present invention pertaining to a power system for a vehicle in which a rotational output of an engine is decelerated and transmitted to a driving wheel by a swash plate type oil hydrostatic non-stage transmission, the inclination angle of a speed change swash plate provided in the swash plate type oil hydrostatic non-stage transmission is varied by a ratio change mechanism to vary the change gear ratio, and the variation of the change gear ratio is detected by a ratio detecting sensor having a detecting member moved in conjunction with the speed change swash plate wherein the ratio change mechanism comprises a ratio change driving shaft parallel with a speed change output shaft of the swash plate type oil hydrostatic non-stage transmission, and the ratio change mechanism is so disposed that a line segment connected between the axes of the ratio change driving shaft and the speed change output shaft is parallel with a mating plane between the crank case and the cylinder.
According to the present invention, the ratio change mechanism is so disposed that the line segment connecting between the center of the ratio change driving shaft and the center of the speed change output shaft is parallel with the mating plane between the crank case and the cylinder, and, therefore, the machining axis for the ratio detecting sensor fitting portion of the crank case is parallel to the cylinder axis. As a result, the machining axis for the ratio detecting sensor fitting portion and the machining axis for the crank chamber are parallel to each other, and the components or portions can be machined from the same direction.
Accordingly, it is needless to once stop machining after machining of the crank chamber, reposition the crank case on jigs, and resume machining for the ratio detecting sensor fitting portion, as in the prior art. Thus, the two works or portions can be machined with a single positioning, so that time and labor for positioning in machining can be reduced, and operability is remarkably enhanced.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.